JP-A-2005-288770 describes an ink-jet printing device in which a sub-tank containing ink to be supplied to a print head is partitioned vertically by a ventilation film (gas permeable film), a part below the ventilation film serves as an ink chamber (liquid supply channel) containing ink, and a part above the ventilation film serves as an air chamber (discharge channel) to which air in the ink chamber is discharged. The air chamber is connected to a deaeration pump with a valve interposed therebetween, and the air in the air chamber and the ink chamber is discharged externally by actuating the deaeration pump with the valve opened to suction the air in the air chamber. By closing the valve after suctioning the air in the air chamber by actuating the deaeration pump, the air chamber is maintained in reduced pressure and then the air flowing in the ink chamber is discharged to the air chamber due to the reduced pressure of the air chamber. Accordingly, it is possible to prevent the air from flowing into the print head together with the ink at the time of supplying the ink from the ink chamber to the print head.
In JP-A-2005-288770, since air flowing in the ink chamber is lighter than the ink, the air is accumulated sequentially from the upper portion of the ink chamber, that is, the portion close to the ventilation film. Accordingly, in JP-A-2005-288770, when a large amount of gas flows in the ink chamber, the gas is accumulated at a position apart from the ventilation film and thus the gas accumulated at the position may not be efficiently discharged to the air chamber.